Honeycomb units for exhaust emission control have metal outer tubes and metal honeycomb structures pressed into and joined to the tubes, as disclosed in JP-B-2709789.
The metal carrier (hereinafter referred to as “honeycomb unit”) disclosed in JP-B-2709789 includes a metal outer tube and a honeycomb structure pressed into and joined to the metal outer tube. The honeycomb structure has a planar sheet and a corrugated sheet placed on the planar sheet and wound together with the planar sheet.
The metal outer tube is brazed to the honeycomb structure through brazing materials at locations between the metal outer tube and the honeycomb structure. The planar sheet is brazed to the corrugated sheet through brazing materials at locations between the planar sheet and the corrugated sheet. The brazing material at each location between the metal outer tube and the honeycomb structure is the same in length as the brazing material each location between the planar sheet and the corrugated sheet.
For the honeycomb unit in JP-B-2709789, the honeycomb structure has a temperature which increases by heat of exhaust gas passing therethrough. This increase in temperature of the honeycomb structure is followed by increase in temperature of the metal outer tube. Likewise, decrease in temperature of the honeycomb structure is followed by decrease in temperature of the metal outer tube.
The brazing materials are arranged without taking account of reaction between the metal outer tube and the honeycomb structure during the change in temperature of the honeycomb structure and the outer tube.
There is a need of brazing material arrangement accommodating the temperature change.